1. Technical Field
The present invention relates to a driver circuit for laser diodes and, more particularly, to a dynamically controlled driver circuit that is capable of reducing overshoot of the driver circuit.
2. Description of the Prior Art
Laser diode driver circuits generally comprise a number of cascaded gain stages comprising differential pairs of GaAs FETs. A final differential output stage is then used to drive the laser diode with an input current signal, I.sub.laser, Conventional driver circuits, as discussed in detail below, are static in their design and generally designed to provide large current values for I.sub.laser, generally in the range of 80-90 mA. However, there are some laser diodes that require drive currents in the range of only 10-20 mA, where these conventional drive circuits result in "overdriving" the laser diode. This results in overshoot on the output signal when data is switching from one logic level to the other and results in chirp of the laser diode output.
Additionally, laser diodes may require different drive currents, as a function of age, to provide the same output signal. That is, laser diodes may require a relatively low drive current (10-20 mA) early in life, then rise to levels of 80-90 mA at end of life. Using a conventional drive circuit with such lasers results in either "over-driving" the laser early in life or "under-driving" the laser later in life. In general, the use of a "static" drive circuit design as is common in the prior art is not suitable for use with laser diodes that have characteristics that change as a function of age.
Lastly, there are various laser diode environments that may result in modifying the drive circuit requirements. For example "uncooled" lasers need to control their drive current to remain at minimal levels, while "cooled" lasers may be able to withstand relatively large drive currents. The same conventional drive circuit is not suitable for use in both applications, requiring that different drive circuits be developed for each situation.
Thus, a need remains in the prior art for a laser diode drive current design that is more robust and capable of use with various laser drive currents.